This invention relates to a high efficiency method for refining waste oils to produce base oil and other valuable products, which includes the steps of separating at least a portion of the base oil constituents (base oil fraction), typically mineral oil suitable for lubrication service with a boiling point usually between 500 and 1100° F., from the various physical contaminants and other hydrocarbon fractions of the waste oil, separating from the base oil fraction a portion of the lower quality molecules such as those containing hetero atoms, unsaturates, polars and aromatics, thereby creating a first high quality marketable base oil stream and a stream wherein the lower quality molecules have been concentrated and thereafter further treating the lower quality base oil stream to at least partially convert the constituents containing hetero atoms, unsaturates, polars and aromatics to higher quality molecules by removing sulfur, oxygen, nitrogen, chlorine constituents and the like and more fully saturating the molecules thereby producing a second marketable quality base oil stream.
Annually large volumes of finished lubricating oils are produced worldwide. Finished lubricating oils are produced by combining base oil (also known as base stock, base lube stock, lube stock, lube oil, lubrication oil and the like) typically a mineral oil with between 18 to 40 carbon atoms and a boiling point between 500 to about 1050° F. with chemical additives which enhance the properties of the base oil making it more suitable for its intended service. The quality, quantity and type of base oil used depend upon the service for which the finished lubricating oil is made.
The quality of the base oil component is typically determined by several factors related to the oil's compositional and physical properties. The American Society for Testing and Materials (ASTM) has compiled ASTM D-6074-99 Standard Guide for Characterizing Hydrocarbon Lubricant Base Oils as a guide for testing the quality of base oil. Similarly, the American Petroleum Institute (API) has prepared Specification API 1509, Engine Oil Licensing and Certification Systems Specification in order to help quantify and categorize base oil quality. The compositional properties relate to actual chemical composition of the base oil, such as the presence of certain contaminants other than hydrogen and carbon in the base oil molecules and the configuration, form or structure of the base oil molecules. The physical properties relate to the performance of the base oils when tested in predefined ways and include such properties as viscosity, flash point, volatility and the like.
API 1509 currently has designated six classifications (“Groups”) of base oil. Groups I, II and III typically classify base oils in accordance with their physical and compositional properties. Groups IV, V and VI typically classify base oil by type; include synthetic oils and the like. Mineral oils derived from waste oil will typically be classified in Groups I, II or III. These Groups are principally distinguished by the concentration of sulfur, percent saturates and viscosity index.
Typically, base oils and finished lubricating oils, by usage and/or handling, become contaminated with oxidation and degradation products, water, fuels, solvents, antifreeze, other oils, fine particulates, additive products and the like. Service can also result in changes in the molecular structure of the oil and/or the chemical additives thereby changing the original nature of the oil. These contaminants or changes may reduce the desired performance of the oils or render the oils unsuitable for use in their intended services and necessitate disposal or replacement with new, uncontaminated oil. Once deemed unfit for use or service, these contaminated oils are typically called waste oil or used oil. Waste oil can be either petroleum or synthetically based oil, that may or may not have been in service and include oils that typically are used as lubricants for engines, turbines and gears, hydraulic fluids, metal working fluids, insulating or cooling fluids, process fluids or the like.
Waste oil is typically collected by a large number of regional waste oil gatherers who collect it from the local sites of utilization or production. In the collection process, a great variety of oils, which were formulated for numerous types of service, are mixed together thereby forming a composite of different types and qualities of base oil, chemicals, contaminants and the like.
With the ever-increasing desire to conserve and manage our petroleum resources in a responsible way, there is renewed focus on the need to recover and re-refine waste oils to recover the base oil contained therein. Currently, the vast majority of the collected waste oil is combined with industrial fuel oils and burned as a combustion fuel. This practice not only contributes significant pollutants to the environment, but also wastes energy and contributes to our dependence on foreign oil. Those most familiar with the problem, including the U.S. Environmental Protection Agency and the American Petroleum Institute, have recognized that re-refining to produce base oil is the highest and best use of the waste oil and the industry has long sought an efficient, economic and environmentally friendly process which is capable of recovering a high percentage of the base oil from the waste oil (high efficiency) and producing a high percentage of high quality products therefrom (high quality).
Several treatment processes have been proposed for creating cleaner burning fuel oils or diesel oils from the waste oil which employ various forms of processing including; thermal cracking U.S. Pat. Nos. 5,362,381, 5,382,328, 5,885,444; distillation U.S. Pat. Nos. 4,101,414, 4,342,645, 5,306,419, 5,814,207, 5,980,698, RE38,366; pyrolysis U.S. Pat. No. 6,132,596; coking U.S. Pat. Nos. 5,143,597, RE36,922 and the like. However, creating fuel oils is not the highest and best use for the waste oil since the energy and intense processing that was undertaken to originally produce the base oil from crude oil or through synthesis processes is lost when the oil is consumed by combustion. Furthermore, the resource itself is lost. Hence, waste oil burning does not fully meet the ultimate objectives of conservation and recovery.
The ideal re-refining process would produce a high percentage of base oil, produce high quality products—both base oil and byproducts, be environmentally friendly and economically viable and commercially sound. While several processes have been proposed for re-refining waste oil into base oil, none are currently capable of meeting all the desired objectives as effectively as the method described hereinafter.
For example, waste oil has long been re-refined to base oil using sulfuric acid to separate contaminants from useful hydrocarbon components followed by treatment with clay, however, few facilities of this type remain due to poor base oil product quality and the generation of large amounts of highly toxic, environmentally hazardous, acid and clay sludge. This type of process has been banned from use in many westernized countries because of these shortcomings.
Waste oils have also been re-refined to base oil utilizing a process known as hydrotreating or hydrofinishing. Several patents describe various derivatives of the process including U.S. Pat. Nos. 4,431,524; 4,432,856; 4,512,878; 4,941,967; 5,045,179 and 5,447,625. This treatment method typically employs some form of distillation to separate a base oil fraction from other contaminants, followed by treatment with hydrogen at elevated temperatures and pressures over a catalyst. While this method has been successful in saturating some aromatics and non-saturated compounds, severe hydrotreating (higher temperatures, pressures, hydrogen concentrations, residence time, etc) is required to sufficiently saturate oil molecules and achieve the physical and compositional properties of higher quality base oils. Unfortunately, these severe processing conditions can result in molecular cracking, which consequently results in base oil yield loss thereby lowering the amount of base oil produced. Therefore, this process is not capable of producing both high quality products (high quality) and high quantity yields (high efficiency). Further, hydrotreating all the base oil fraction is expensive typically resulting in marginal economics.
Another method of re-refining waste oil to base oil utilizes solvent extraction. This process also suffers from a yield/quality trade-off. U.S. Pat. Nos. 4,021,333; 4,071,438; 4,360,420; 6,117,309; 6,319,394; 6,320,090 and 6,712,954 describe various processes involving some form of distillation followed by solvent extraction. U.S. Pat. Nos. 4,302,325 and 4,399,025 describe extraction processes on base oil fractions, however derived. In these processes, a portion of the contaminated base oil molecules (polars, aromatics, heteroatoms, unsaturates) are separated from the base oil fraction using liquid/liquid extraction. This creates a purified base oil stream (raffinate) and an extract oil stream (extract) wherein some of the contaminated molecules are concentrated. The efficacy of separation of quality base oil from contaminated molecules is determined by several variables including temperature, treatment ratio, residence time, contact, and the presence of other fluids added to the oil and solvent. In the extraction process there is continual trade-off between selectivity (the amount of good base oil taken with the extract) and purity (percent of contaminated base oil molecules left in the raffinate).
Typically solvent extraction processes are effective at removing some of the aromatics, polars and unsaturated compounds. However, to reach the desired level of purification necessary for higher quality standards using known processes, the selectivity of the solvent must be reduced whereby both contaminated molecules as well as good molecules are taken by the solvent, which significantly reduces the yield of base oil. Therefore, there is an inherent trade-off between quality and yield so that in order to get high quality base oil, yield quantity may be reduced (see U.S. Pat. No. 6,712,954).
As previously noted, known processes of this type are capable of producing either high quality or high yield, but not both. This is due to the nature of the waste oil, which consists of a wide variety of types, qualities and contaminants and the consequential trade-off between quality and quantity that is typically inherent in these processes. Furthermore, most known process of this type typically can only produce a Group I base oil. An additional disadvantage of this process is that the extract formed by solvent extraction of waste oil is also prone to reformation assumed to be polymerization. This polymerization is believed to be catalyzed by acid and can be reduced through addition of base or blending with fuel oil or other anti-polymer chemicals thereby adding to the overall production cost. Furthermore, the resulting product is a low quality base oil, which may be difficult to market.